Effects of vegetation on bacterial communities, carbon and nitrogen in dryland soil surfaces: implications for shrub encroachment in the southwest Kalahari

Spatial organisation of fungi in soil biocrusts of the Kalahari is related to bacterial community structure and may indicate ecological functions of fungi in drylands

Biological soil crusts, or biocrusts, are microbial communities found in soil surfaces in drylands and in other locations where vascular plant cover is incomplete. They are functionally significant for numerous ecosystem services, most notably in the C fixation and storage due to the ubiquity of photosynthetic microbes. Whereas carbon fixation and storage have been well studied in biocrusts, the composition, function and characteristics of other organisms in the biocrust such as heterotrophic bacteria and especially fungi are considerably less studied and this limits our ability to gain a holistic understanding of biocrust ecology and function. In this research we characterised the fungal community in biocrusts developed on Kalahari Sand soils from a site in southwest Botswana, and combined these data with previously published bacterial community data from the same site. By identifying organisational patterns in the community structure of fungi and bacteria, we found fungi that were either significantly associated with biocrust or the soil beneath biocrusts, leading to the conclusion that they likely perform functions related to the spatial organisation observed. Furthermore, we showed that within biocrusts bacterial and fungal community structures are correlated with each other i.e., a change in the bacterial community is reflected by a corresponding change in the fungal community. Importantly, this correlation but that this correlation does not occur in nearby soils. We propose that different fungi engage in short-range and long-range interactions with dryland soil surface bacteria. We have identified fungi which are candidates for further studies into their potential roles in biocrust ecology at short ranges (e.g., processing of complex compounds for waste management and resource provisioning) and longer ranges (e.g., translocation of resources such as water and the fungal loop model). This research shows that fungi are likely to have a greater contribution to biocrust function and dryland ecology than has generally been recognised.

Phosphorus deficiency is the main limiting factor for re-vegetation and soil microorganisms in Mu Us Sandy Land, Northwest China

Long-term drought induced by low rainfall leads to environmental degradation of land in arid and semi-arid regions. In past decades, re-vegetation of degraded sandy soils to prevent soil erosion has been widely employed, including in Mu Us Sandy Land, which suffers from severe soil erosion. However, it remains unclear how re-vegetation affects soil properties and soil microbes after long restoration periods. In this study, typical plots planting Artemisia ordosica and Salix psammophila were selected to investigate the influence of plant types on soil properties; an area of bare sandy land was used as a control. The results show that re-vegetation increased soil organic carbon (C), total nitrogen (N), soil microbial carbon, microbial nitrogen and soil organic acid, while decreasing soil total phosphorous (TP) content significantly, resulting in increased C/P and N/P ratios. Correlation analysis showed that TP was negatively correlated with oxalic acid (OA) and acetic acid (AA), indicating that increased AA and OA content could accelerate the active utilization of phosphorus and induced low TP in soil. Re-vegetation with A. ordosica significantly decreased the microbial diversity of topsoil. The redundancy analysis showed that TP was main index in affecting microbes. These results that lower P content, higher C/P and N/P ratio and influence of TP on microbes suggest that phosphorus is the main limiting factor for re-vegetation and growth of soil microorganisms. In the future, strategies for the development of sustainable ecosystems in regions suffers from severe soil erosion should consider phosphorus supplementation.

Species Diversity and Carbon Sequestration Oxygen Release Capacity of Dominant Communities in the Hancang River Basin, China

Plants play an important role in the storage of organic carbon as a carbon reservoir, mainly reflected in the absorption of carbon dioxide and the release of oxygen by plants through photosynthesis, which plays an important role in regulating regional carbon balance. This study aimed to explore the pattern of dominant vegetation species diversity in small basin ecosystems, analyze the photosynthetic carbon sequestration characteristics of dominant vegetation and its carbon sink potential, and use the Hancang River Basin as the research area to obtain species abundance data using the sampling method. The community characteristics were analyzed from the aspects of species richness, α diversity index, dominant population spatial pattern, and interspecific correlation. Fifteen typical plants were selected; the photosynthetic carbon sequestration capacity of the plants was measured and quantified, and the correlation of the nitrogen ecological measurement characteristics of the leaves were analyzed. The results showed that all 15 dominant vegetation types were clustered, and the aggregation intensity and interspecific correlation were closely related. Spearman’s analysis showed that the dominant vegetation community structure and diversity in the Hancang River Basin were unstable, and there may be strong interspecies competition and frequent species replacement in the future succession process. The daily trend of the net photosynthetic rate of dominant vegetation tended to be bimodal or nearly bimodal, and the peak generally appeared at 10:00 or 14:00. The leaf area index of the dominant species was greater than 3.0, of which the largest was Platanus acerifolia at 5.31. The smallest was Hemerocallis fulva (L.) L., which was 1.16. The average carbon sequestration per unit leaf area and unit land area of the dominant species was 10.02 g·m−2·d−1 and 42.35 g·m−2·d−1, respectively, and the average oxygen release was 7.29 g·m−2·d−1 and 30.8 g·m−2·d−1, respectively. The average maintenance breathing volume of the leaves was 2.94 μmol CO2 m−2s−1. Comprehensive analysis of the ecological restoration process of the Hancang River Basin should focus on Platanus acerifolia, Prunus serrulata var. lannesiana, Prunus cerasifera, Ligustrum lucidum, and other highly efficient carbon sequestration plants, to carry out rational planting and to build a multilayer composite configuration of forest shrub and grass models to improve the ecological problems of the basin.

Biochemical composition and function of subalpine shrubland and meadow soil microbiomes in the Qilian Mountains, Qinghai-Tibetan plateau, China

Microorganisms participate in the soil biogeochemical cycle. Therefore, investigating variations in microbial biomass, composition, and functions can provide a reference for improving soil ecological quality due to the sensitivity of microorganisms to vegetation coverage changes. However, the differences in soil microorganisms between shrubland and meadow have not been investigated in ecologically vulnerable subalpine areas. This study aimed to investigate the biochemical composition and functions of the soil microbial community under two shrublands and a meadow at high altitudes (3,400-3,550 m). Three sites under two shrublands, Rhododendron thymifolium (RHO) and Potentilla fruticosa (POT), and one meadow dominated by Kobresia myosuroides (MEA), were selected on the southern slope of the Qilian Mountains on the northeastern edge of the Qinghai-Tibetan Plateau, China. Soil physicochemical properties, the microbial community composition expressed by the phospholipid fatty acid (PLFA) biomarker, and enzyme activities were analyzed as well as their relationships. The results showed that water holding capacity and the soil carbon, nitrogen, and potassium content in RHO and POT were higher than those in the MEA. Moreover, the soil active carbon, dissolved organic carbon, total nitrogen, and dissolved total nitrogen content in RHO were higher than those in POT. The abundance of total PLFAs, bacteria, and fungi beneath the shrublands was considerably higher than that in the MEA. The PLFA abundance in RHO was significantly higher than that in POT. The fungal-to-bacterial ratio of RHO and POT was significantly higher than that in the MEA. The activities of β-glucosidase, cellobiohydrolase, and leucine aminopeptidase were the highest in RHO among the three vegetation types, followed by POT and MEA. The redundancy analysis indicated that the biochemical composition of the soil microorganisms and enzyme activities were driven by total nitrogen, dissolved organic carbon, water holding capacity, and soil organic carbon. Therefore, shrublands, which have higher biomass, can improve soil moisture status, increase soil carbon and nitrogen content (especially active carbon and active nitrogen), and further increase the abundance of total PLFAs, bacteria, and fungi. The increase of microbial biomass indirectly enhances the activity of relevant soil enzymes. The variations in PLFA abundance and enzyme activities can be attributed to shrub species, especially evergreen shrubs, which create more favorable conditions for soil microorganisms. This study provides a theoretical basis for investigating the soil biogeochemical cycle and a scientific basis for soil management and vegetation restoration in the subalpine regions.

Specific Plant Mycorrhizal Responses Are Linked to Mycorrhizal Fungal Species Interactions

Effects of arbuscular mycorrhizal fungi (AMF) on plants span the continuum from mutualism to parasitism due to the plant-AMF specificity, which obscures the utilization of AMF in the restoration of degraded lands. Caragana korshinskii, Hedysarum laeve, Caragana microphylla, and Poa annua are the most frequently used plants for revegetation in Kubuqi Desert, China, and the influence of AMF on their re-establishment remains to be explored further. Herein, using a greenhouse experiment, we tested the plant-AMF feedbacks between the four plant species and their conspecific or heterospecific AMF, retrieved from their rhizosphere in the Kubuqi Desert. AMF showed beneficial effects on plant growth for all these plant-AMF pairs. Generally, AMF increased the biomass of C. korshinskii, H. laeve, C. microphylla, and P. annua by 97.6, 50.6, 46.5, and 381.1%, respectively, relative to control. In addition, the AMF-plant specificity was detected. P. annua grew best, but C. microphylla grew worst with conspecific AMF communities. AMF community from P. annua showed the largest beneficial effect on all the plants (with biomass increased by 63.9-734.4%), while the AMF community from C. microphylla showed the least beneficial effect on all the plants (with biomass increased by 9.9-59.1%), except for P. annua (a 292.4% increase in biomass). The magnitude of AMF effects on plant growth was negatively correlated with the complexity of the corresponding AMF co-occurrence networks. Overall, this study suggests that AMF effects on plant growth vary due to plant-AMF specificity. We also observed the broad-spectrum benefits of the native AMF from P. annua, which indicates its potential utilization in the restoration of the desert vegetation.